The subject of the present invention is a process for the preparation of N-(1,1-dimethylethyl)-4-[[5xe2x80x2-ethoxy-4-cis-[2-(4-morpholino)ethoxy]-2xe2x80x2-oxospiro[cyclohexan- 1,3xe2x80x2-[3H]indol]-1xe2x80x2(2xe2x80x2H)-yl]-sulfonyl]-3-methoxybenzamide (SR 121463) of formula I 
and its salts, compounds having vasopressine V2 antagonistic effect.
According to patent application WO 9715556 the compound of formula I is prepared by reacting the spiro/cis-4-(beta-morpholino-ethyloxy)cyclohexan-1,3xe2x80x2-(5xe2x80x2-ethoxy)-[3H]indol-2xe2x80x2[1xe2x80x2H]one of formula II 
with the 2-methoxy-4-(N-t-butylaminocarbonyl)benzenesulfonyl chloride of formula III 
using potassium-t-butylate in tetrahydrofuran.
Because of the applied solvent (tetrahydrofuran) and reaction temperature (between xe2x88x9260xc2x0 C. and 40xc2x0 C.) it is not easy to carry out the process under industrial conditions, the yield is low, the product is contaminated, its purification requires repeated crystallization.
To our surprise, we have found that by stirring in dimethyl sulfoxide at room temperature the reaction proceeds in very good yield (85-92%). The work-up procedure is simple, while in the original process the product is obtained by extraction, in the present process the base precipitates on diluting the reaction mixture with water, and it can be filtered off. The purity of the resulting base is 93-96% and the salt formed from it is appropriately pure.
In accordance with the above, the subject of the invention is a process for the, preparation of the compound of the formula I 
and the salts thereof, by reacting the compounds of the formula II 
and III, 
which comprises carrying out the reaction in dimethyl sulfoxide at a temperature between 10xc2x0 C. and 40xc2x0 C., preferably at room temperature and transforming the resulting base of formula I into its salt by a method known per se.